This invention relates to a resetting type of thermally responsive valve means which is useful in switching negative and positive pressure circuits from closed to open and then to closed state in sequence (or from open to closed and then to open state) in response to a unidirectional change in temperature through two predetermined temperature levels while assuring prompt closing or opening of the valve means at precisely predetermined temperatures.
Generally speaking, thermally responsive valves of this type are useful in emission control systems of automobiles where the use of valve means of the wax operating type has been previously proposed. However, wax operating valves are commonly subject to a loss of wax when subjected to overpressures and such loss of wax tends to change the operating temperatures of the valve means. Wax operating valves are also of complicated structure having a relatively high production cost and are thus not adapted for low cost mass production.
It is an object of this invention to provide a thermally responsive valve having dual point temperature response which eliminates the conventional defects of such valves, which has a compact outer appearance and a simple structure, which does not have to be repaired frequently, and which can be easily manufactured.
It is also an object of this invention to provide such a thermally responsive valve which has a high degree of resistance to vibration so that it is adapted for use in automotive emission control systems such as in ignition time control devices and the like. It is also an object of the invention to provide such a valve which is adapted to be positioned in heat-transfer relation to an object such as an engine block of an automobile so that the valve is adapted to be opened and closed in response to increases and decreases in engine block temperature and in which the flow of fluid through the valve is controlled smoothly in response to such increases and decreases in block temperature. It is a further object to provide such valve means adapted to switch fluid flow between passages from open to closed and then to open state, or from closed to open and then to closed state, in sequence in response to unidirectional temperature change including a unidirectional temperature increase or an unidirectional temperature decrease over a wide range.
Briefly described, the novel and improved thermally responsive valve of this invention comprises a main valve body which is equipped with two openings. These openings are connected with an internal operating space in the valve body by separate internal passages in the body. Two dish-shaped bimetal pieces are arranged in spaced relation to each other within the internal operating space in the valve body to divide that space into three sections. An annular wave-spaced spring is arranged within the internal operating space between the two bimetal pieces for holding the pieces in said spaced relation to each other. Each of the bimetal elements is adapted to reverse or invert its dish-shape in response to a change in temperature thereof and valve seats are arranged between the internal operating space and passages leading to the valve openings.
The bimetal pieces are arranged within the operating space to engage and disengage respective valve seats as the bimetal pieces reverse or invert their dish-shape in response to temperature change. Where the valve body is provided with two openings connected to the internal operating space by respective passages and with valve seats between the internal space and the respective passages, the bimetal pieces are selected so that, in response to unidirectional temperature change through two temperature levels, one of the bimetal pieces engages a valve seat to close the valve, both bimetal pieces are disengaged from the valve seats to open the valve, and the other bimetal piece engages a valve seat to reclose the valve in sequence, the valve opening and closing occurring promptly as the valve temperature passes through the respective two temperature levels. Alternately, where the valve body has two passages connecting one of the openings to the internal operating space and has valve seats between the internal space and each of these two passages, the bimetals are selected so that a first bimetal engages a valve seat while the second bimetal piece is disengaged from a valve seat to open the valve, both bimetal pieces engage valve seats to close the valve, and then the second bimetal piece engages a valve seat while the first bimetal piece is disengaged from a valve seat to reopen the valve in sequence.